2022 day 11 part 2

lachlanroche · lachlanroche · commit c4b01eb46c95 · 2022-12-11T15:49:35.000+10:00
diff --git a/aoc22.playground/Pages/Day11.xcplaygroundpage/Contents.swift b/aoc22.playground/Pages/Day11.xcplaygroundpage/Contents.swift
@@ -3,5 +3,6 @@
 import Foundation
 
 part1()
+part2()
 
 //: [Next](@next)
diff --git a/aoc22.playground/Pages/Day11.xcplaygroundpage/Sources/Day11.swift b/aoc22.playground/Pages/Day11.xcplaygroundpage/Sources/Day11.swift
@@ -88,5 +88,62 @@ public func part1() -> Int {
 }
 
 public func part2() -> Int {
-    0
+    var monkeys = [Monkey]()
+    var id = 0
+    var items = [Int]()
+    var op = Operation.plus
+    var constant = 0
+    var divisible = 0
+    var ifTrue = 0
+    var ifFalse = 0
+    for line in stringsFromFile() {
+        if line.hasPrefix("Monkey ") {
+            id = Int(line.replacingOccurrences(of: ":", with: "").split(separator: " ").last!)!
+        } else if line.hasPrefix("  Starting items:") {
+            items = line.replacingOccurrences(of: ", ", with: " ").split(separator: " ").dropFirst(2).compactMap { Int($0)! }
+        } else if line.hasPrefix("  Operation") {
+            if line.contains("old * old") {
+                op = .square
+                constant = 1
+            } else {
+                constant = Int(line.split(separator: " ").last!)!
+                op = line.contains("old + ") ? .plus : .multiply
+            }
+        } else if line.hasPrefix("  Test") {
+            divisible = Int(line.split(separator: " ").last!)!
+        } else if line.hasPrefix("    If true") {
+            ifTrue = Int(line.split(separator: " ").last!)!
+        } else if line.hasPrefix("    If false") {
+            ifFalse = Int(line.split(separator: " ").last!)!
+            monkeys.append(Monkey(id: id, items: items, op: op, constant: constant, divisible: divisible, ifTrue: ifTrue, ifFalse: ifFalse))
+        }
+    }
+    
+    let lcm = monkeys.reduce(1) { $0 * $1.divisible }
+    
+    func inspect(monkey id: Int) {
+        let items = monkeys[id].items
+        monkeys[id].items = []
+        for item in items {
+            var worry = item
+            worry = monkeys[id].op.apply(worry: worry, constant: monkeys[id].constant)
+            worry %= lcm
+            if worry % monkeys[id].divisible == 0 {
+                monkeys[monkeys[id].ifTrue].items.append(worry)
+            } else {
+                monkeys[monkeys[id].ifFalse].items.append(worry)
+            }
+            monkeys[id].inspections += 1
+        }
+    }
+    
+    for _ in 0..<10000 {
+        for i in 0..<(monkeys.count) {
+            inspect(monkey: i)
+        }
+    }
+    
+    monkeys.sort { $0.inspections > $1.inspections }
+    
+    return monkeys[0].inspections * monkeys[1].inspections
 }
